Chromosomal translocations play a vital role in oncogenesis and are major factors in the etiology of both solid tumors and leukemia's. Despite the fact that translocations may be etiologic in as many as 20% of all cancers, our understanding of how the translocations arise remains remarkably undeveloped. It has been suggested that interchromosomal translocations are most likely to occur between chromosomes that are in close proximity with one another. Thus, in order to understand how translocations occur, it is important to study the normal spatial configuration of the nucleus. It is our hypothesis that the reason that specific chromosome translocations, such as RUNX1/ EVI1 in acute myeloid leukemia, occur in cancer is due to the fact that these chromatin regions often participate in long-range interactions in normal cells. There are a number of important gaps in our understanding of chromosomal translocation in cancer that will be approached in this grant proposal: Are long-noncoding RNAs and chromatin proteins needed to maintain long-range chromosomal interactions in normal cells, and are these structural elements deranged in cancer? Can long-range interactions be directed by modulating the factors that maintain gene looping, and can translocations occur in the absence of specific long-range interactions? The RUNX1 gene complex in acute myeloid leukemia has been selected as the model system for studying chromosomal translocations, as it is likely that the principles that will be discovered will be applicable to cancers in general. AML tissues that are de-identified are readily available in Tissue Banks at the affiliated institution. The RUNX1 gene complex was chosen as RUNX1 is frequently involved in a variety of chromosomal translocations in patients with AML. A RUNX1-intragenic long noncoding RNA, RUNXOR that is required for RUNX1-associated long-range interactions in normal cells was discovered and characterized in the PI's laboratory. RUNXOR can serve as the model for other lncRNAs involved in long-range chromatin interactions. Moreover, RUNX1 and RUNXOR abundance can be manipulated by chemotherapeutic drugs in vitro. Using novel epigenetic techniques developed in the PI's laboratory, the studies outlined in this grant proposal will yield new knowledge about the regulation of nuclear architecture through long-range chromatin interactions in normal cells and in cancer. Cancer is a major cause of morbidity and mortality in the Veteran population. By studying how lncRNAs and proteins control these interactions and translocations, a greater understanding of the various molecular steps in the translocation process will be achieved. This can provide important guidance in the design of better cancer therapies, and may help in decreasing the occurrence of secondary translocation-initiated tumors that occur as a major side-effect of cancer chemotherapy. Ultimately, we hope to be able to translate these studies into therapeutic advances that will advance the health of our Veterans.